Webs, such as thermoplastic films, have a variety of uses including component materials of absorbent articles (such as topsheets and backsheets), packaging (such as flow wrap, shrink wrap, and polybags), trash bags, food wrap, dental floss, wipes, electronic components, and the like. For many of these uses of webs, it can be beneficial for the web to have a textured, three-dimensional surface which can provide the surface of the web with a desirable feel (e.g., soft, silky), visual impression, and/or audible impression, as well as one or more desirable properties, such as improved fluid handling or strength.
Webs exhibiting a desirable feel can be made via a vacuum forming process, wherein a precursor web is heated and placed over a forming structure. Then a vacuum forces the precursor web to conform to the texture of the forming structure. Vacuum forming processes are typically limited with respect to the amount of pressure capable of being exerted onto a precursor web and hence are inefficient due to the necessary heating step and the limited pressures generated.
Webs exhibiting a desirable feel can also be made via a hydroforming process, wherein a precursor web is placed over a forming structure and high pressure and high temperature water jets force the precursor web to conform to the texture of the forming structure. A hydroforming process, although capable of producing soft and silky polymeric webs, is typically a costly and inefficient process involving the use of high pressure and high temperature water jets and subsequent drying steps, including dewatering steps.
Webs exhibiting a desirable feel can also be made via an embossing process, wherein a substrate is mechanically worked to cause the substrate to conform under pressure to the depths and contours of a pattern engraved or otherwise formed on an embossing roll. Embossing processes typically require heating and cooling steps which add undesirable cost and inefficiency, as well as complexity, to the process. In addition, such embossing processes typically involve relatively large dwell times, which can result in slow, inefficient processes. Or, processes are known wherein a substrate is placed between a forming structure and a compliant material, such as rubber, to enable embossing at relatively low temperatures, as described in US 2010/0230857 and US 2010/0230858. Such processes require high pressure and deformations resulting in equipment wear and reduced lifetime.
While various processes to make textured webs are known, these processes have numerous drawbacks, such as cost, complexity, speed of manufacturing, difficulty creating small tooling, durability of tooling, predictable results, etc. Solid state processes using tooling with two mated, rigid structures have the benefits of low cost, high speed, and durable tooling. However, these processes have been limited to relatively large distances between forming elements as well as relatively large structures; it is difficult to impart relatively small scale texture to precursor webs using conventional forming structures. Further, the ability to make, with solid state formation techniques (generally, any process which occurs at a temperature below the melt point of the polymer or material being processed), a micro-textured web comprising three-dimensional features having either open- or closed-distal ends and location-controlled thinning has not been described.
Accordingly, there remains a need to make micro-textured webs, including formed film webs, using low cost, high speed apparatuses. There is a desire for processes and apparatuses that are capable of forming new structures in webs that provide the webs with a micro-texture, and thus, a desirable feel, visual impression, and/or audible impression as well as additional properties. In the case of webs used in absorbent articles, such new processes and apparatuses may include those that provide a single portion of the web with dual, or more, properties (such as improved softness, fluid handling, or other properties) in a predetermined location on the web. A need also exists for processes and apparatuses that will allow a web to be deformed multiple times while maintaining control over the registration of the deformations in the web. One objective of the present invention is to impart sufficient web tension and/or friction between a web and a pair of forming structures to allow a micro-textured web to form.